The FBI has 'strong preliminary indications' that Border Patrol agent Nicholas Ivie's killing in Arizona was a friendly fire accident.

BISBEE, Ariz. — There are "strong preliminary indications" that the shooting of two U.S. Border Patrol agents, one of whom died, was a friendly fire incident that occurred as they investigated a report of suspicious activity in rugged terrain south of Tucson, FBI officials said Friday.

James L. Turgal Jr., FBI special agent in charge in Arizona, said it appeared that Agent Nicholas J. Ivie was killed and another agent wounded as "the result of an accidental shooting incident involving only the agents."

Ivie was fatally shot early Tuesday while he and two colleagues were patrolling near the Arizona town of Naco, in an isolated corridor frequented by Mexican drug cartel members and illegal border crossers.

"The FBI is utilizing all necessary investigative, forensic and analytic resources in the course of this investigation," Turgal said in a statement. "At the appropriate time further information will be provided."

One of the agents was released from a hospital after being treated for gunshot wounds. The third agent was not injured. Turgal cautioned that federal investigators had reached no conclusions about what happened.

Shawn Moran, vice president of the National Border Patrol Council, said he could not confirm the friendly fire information but noted that agents often converge on a scene from different directions. Rugged terrain, lack of lighting and a barrage of gunfire can make for chaotic and confusing circumstances, he added.

For instance, San Diego-area agents are believed to have shot at each other during a confrontation about a decade ago, though no one was injured.

"When gunshots start, you always want to know where the friendly forces are, and sometimes in the heat of battle it's hard to keep track," Moran said. "It doesn't make the death of Agent Ivie less heroic or less tragic. It's a horrific incident."

Investigators scoured the desert area on horseback and all-terrain vehicles and with helicopters in the days after the shooting.

Gun-trace documents from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives obtained by The Times show that a high-powered rifle and a handgun were found near the shooting scene, though it was not clear whether they were connected to the incident.

A .223 Bushmaster rifle, seized on Wednesday, was "recovered in Mexico in the vicinity where Border Patrol agent was murdered," according to one of the documents. It says the weapon was purchased in the United States but does not specify where.

A .38-caliber Titan Tiger revolver was recovered separately Tuesday in Mexico, also near the Naco area, a second document says. That trace record included this alert: "Urgent High Profile Border Agent Shot."

The record says the weapon was originally purchased in February 2009 from the Frontier Gun Shop in Tucson.

Ivie, a six-year Border Patrol agent, was killed not far from where fellow Agent Brian Terry was slain in December 2010. Two weapons recovered from that shooting were later traced to the ATF's failed Fast and Furious gun-tracking operation, which allowed illegal gun purchases on the border in an attempt to snare Mexican drug cartel leaders.

There was no suggestion in the gun-trace records that the two weapons found after Ivie was killed were tied to Fast and Furious.

On Friday morning, Homeland Security Secretary Janet Napolitano and Border Protection Deputy Commissioner David Aguilar visited the Ivie family in Sierra Vista, Ariz., to offer their condolences. They also spoke with agents at the Border Patrol station in Naco, now named after Terry.

Jeffrey D. Self, a top Customs and Border Protection commander in Arizona, said he advised Ivie's family that investigators believed it was possible the shootings were "a tragic accident."

"I explained to Agent Ivie's family that if the investigation ultimately reaches that conclusion, it changes none of the following facts," Self said. "Agent Ivie gave the ultimate sacrifice and died serving his country. He died in the line of duty and will be honored as such for his final act of service."

"The fact is, the work of the Border Patrol is dangerous," Self added.

Kevin Goates, a spokesman for the Ivie family, would not elaborate on the visit but said the family has "very strong feelings" about the situation, including Friday's developments.